There is a need for processes that can capture CO2 from the flue gases emitted from a variety of industrial processes e.g. from power, cement, lime, iron & steel, petroleum processing, in order to mitigate global warming from the CO2 emissions from such installations. The separation of CO2 from combustion gases is the first step in a Carbon Capture and Sequestration (CCS) process in which the CO2 is separated, compressed to a high density fluid, transported and sequestered in deep saline aquifers, depleted oil and gas fields, deep coal seams, or deep ocean reservoirs. Because of the very large investment associated with industrial infrastructure in the industrial processes, it is preferable that the separation process can be retrofitted to capture the flue gases emitted from such existing infrastructure, in a process referred to as Post Combustion Capture (PCC).
While there are many existing chemical and physical processes for separating CO2 from flue and fuel gases, the barriers to widespread adoption of any such process are technical, economic and environmental. For power plants, a viable PCC CCS process is typically expected to meet the following specifications:                The cost of CO2 separation, including compression to the high density fluid, is low, e.g. less than US$20 tonne-1; and        The efficiency of capture of CO2 from the flue gas is high, e.g. exceeds 90%; and        The efficiency of production of electricity (Electrical Power Output to Lower Heat Value of the Fuel) is reduced as little as possible, and preferably not more than 5%; and        There is little or no additional environmental harm.        
Sceats (“System and Method for Processing Flue Gas” PCT/AU2009/000613) describes a CaO Looping system, herein called the Endex Configuration, which can meet these specifications. The conventional approach to CO2 separation by CaO Looping was described by Heesink et al (A. B. M. Heesink and H. M. G. Temmink “Process for removing carbon dioxide regeneratively from gas streams” PCT WO 1994/01203) in 1994 for removing CO2 from flue gas and fuel gas streams. The Endex Configuration overcomes the major hurdles in the application of CaO Looping identified in a large body of scientific work since 1994.
Use of a gas turbine power train to provide compressed flue gas to a CO2 separation system before expansion to atmospheric pressure is described by T. Christensen, K. Borseth and H. Fleishner, “Method and Plant for Separation of CO2 from the exhaust from combustion of carbonaceous materials” WO 2004/02645). The principal teaching of that patent application was to describe a means of cooling the hot compressed flue gas so that a low temperature CO2 separation can be used, and reheating the scrubbed compressed flue gas so that the compression, energy can be released in a turboexpander to generate a net output of electrical power. The cooling and reheating will be associated with an energy penalty, and is potentially useful for a number of high pressures, low temperature CO2 separation technologies. However, the described process is not suitable for high pressure, high temperature CO2 separation technologies such as the Endex Configuration.
The insertion of a CO2 Separation System between the stages of a multistage turboexpander in a gas turbine power plant has been described by S. M-N Hoffman and M. Bartlett, “Systems and Methods for Power Generation with Carbon Dioxide Isolation”, US Pat Appl. 2008/0104939. However, the separation of CO2 in the power plant as described by US Pat Appl. 2008/0104939 is generally not effective because gas turbine plants have a very low CO2 partial pressure such that the efficiency of CO2 capture even at the high pressures available between the turboexpander segments makes the achievement of high (e.g. 90%) capture target difficult to achieve.
A need therefore exists to provide a system and method to remove CO2 from atmospheric flue gas streams that seeks to address at least one of the above mentioned problems.